In the above two disclosures a rotary rock bit is described having rolling bearing elements housed between facing opposed annular races on the axle portion of the bit body and the rotary cutter journaled thereon. The bearing elements are caged in a semi-solid permeable porous plastic bracelet having lubricant in the pores that provides in situ lubrication to the bearing elements during use and at least initially provides an annular seal for the bearing cavity to prevent the ingress of external debris into the cavity.
However, in that the material was exposed to a pressurized bearing conditioning fluid (such as pressurized air) the combined effects of the loading action on the material, the loss in volume as the lubricant was depleted therefrom, and the abrasive action of the external debris ultimately resulted in the gradual extrusion of the material from the bearing cavity, resulting in the bearing cavity ultimately becoming open to the flow of the bearing conditioning fluid therethrough to cool and lubicate the bearing and prevent debris from entering the cavity.
Although the above structure considerably extended the effective bearing life of such a bit, it still had a finite life that resulted quite often in bearing failure prior to the cutting structure becoming dull. Also, it is known in the prior art, and particularly common in rotary bits for drilling oil and gas wells wherein the circulating fluid is a "mud", to have a lubricant reservoir providing lubricant communication to the bearings and having an annular elastomeric seal at the mouth of the cone cutter bore to seal the bearing cavity from external material and seal the lubricant in. However, because of seal fatigue failure due to the pumping pulsating mechanical forces transferred to the seal from the relative motion between the arm journal and cone cutter, the seal is a life limiting factor and the seal effectiveness has occasionally been quite short resulting in premature bearing failure from loss of lubricant and ingress of debris.